After a long period of basic research and clinical monitoring, it is found that diseases such as breast cancer, ovarian cancer, osteoporosis, schizophrenia and Alzheimer's disease are closely related to the abnormality of the estrogen signaling pathway. Estrogen is a steroid hormone secreted by the endocrine system, and plays an important role in the reproductive system, bone tissue, cardiovascular system, immune system and central nervous system. Estrogen signal transduction system plays an important role in the regulation of cell growth, differentiation and apoptosis. The occurrence and development of estrogen-dependent tumors, such as breast cancer, ovarian cancer, and endometrial cancer, are closely related to estrogen. Currently, the main chemotherapy for breast cancer is the use of antiestrogen agents, such as Tamoxifen. However, Tamoxifen exerts estrogen agonist properties in the uterus, thereby stimulating cancer cells in the uterus. Due to these serious side effects, it is imperative to seek a new safe and effective treatment.
One important protein of the estrogen signaling pathway is estrogen receptor (ER). ER is a steroid hormone receptor, and belongs to a ligand-activated transcription factor of the nuclear receptor superfamily that contains two subtypes: ERα (discovered in 1950) and ERβ (discovered in 1996), encoded by different genes, respectively. ERα and ERβ show a high degree of similarity at the amino acid level, and their similarity in the DNA binding domain is up to 97%, and the similarity in the ligand binding domain is up to 56%, but only 24% low homology in the N terminus. ER contains 6 domains from A to F, which comprise four main functional areas. The functional area of the N terminal A/B domain is a ligand independent transcriptional activation function AF-1, and AF-1 has a constitutive activity. The transcription of target genes is activated by interaction with basic transcription factors, reactivation factors and other transcription factors. There are multiple phosphorylation sites in this function, and it is reported that the role of AF-1 depends on protein phosphorylation. The DNA binding domain (DBD) composed of the C domain is highly conservative and contains 2 zinc finger domains that can specifically bind to the target DNA, simultaneously, and this domain plays an important role in the dimerization of receptors. The D domain is a hinge region that connects the DBD and the ligand binding domain (LBD), with low conservatism (only 30% homology between two subtypes). The ligand binding domain (LBD) composed of the C terminal E domain determines the specific binding of ER to ligands such as estrogen, selective estrogen receptor modulator (SERM), and selective estrogen receptor downregulator (SERD). LBD has a ligand dependent transcriptional activation function AF-2, which has a synergistic reaction with AF-1 to exert ER receptor's role in activating the transcription of target genes. At the same time, LBD has a strong dimerization interface and still can function without ligands. Therefore, LBD is the key site for receptor dimerization.
ERα is mainly distributed in the uterus, ovary, testis, pituitary, kidney, epididymis and adrenal gland, while ERβ is mainly distributed in the prostate, ovary, lung, bladder, brain and blood vessels. Due to the serious side effects of full agonists or full antagonists, the study of SERM arises. The “selectivity” means that SERM acts as an agonist in some tissues such as bone, liver and the cardiovascular system that are rich in ERβ, whereas it acts as an antagonist in some other tissues such as mammary glands. In the uterus, the significant region of ERα, it can be either an agonist or antagonist. So far, commercially available SERMs include Tamoxifen, Raloxifene, Bazedoxifene, Toremifene and the like. However, studies have found that commercially available SERMs still have serious side effects, for example, the long-term use of Tamoxifen and Toremifene can cause endometrial hyperplasia, polyps and endometrial cancer, and the common side effects of Raloxifene include hot flashes, leg pain, breast tenderness and venous thrombosis and the like. Therefore, the research and development of new compounds are still urgent problems to be solved.
Tamoxifen belongs to a class of compounds known as selective estrogen receptor modulators (SERMs), and has the ability to stabilize ERα and slightly upregulate the level of ERα receptors. In contrast, fulvestrant induces rapid degradation of ERα and intensifies the blockage of the ER receptor signaling pathway, and such compounds are called selective estrogen receptor downregulators (SERDs). The differences in the mechanisms of actions of these SERMs and SERDs seem to be the mechanisms responsible for the resistance of these compounds. A large number of tumors that are tamoxifen resistant and ER positive are still sensitive to fulvestrant. It is found clinically that SERDs such as fulvestrant can effectively treat some breast cancers that are ERα positive and tamoxifen resistant. Therefore, the compounds responsible for degradation of ERα can be used to prolong the duration of efficacy in breast cancer patients successfully treated with anti-estrogen therapy, whereas different SERMs, aromatase inhibitiors and SERDs can be used successively.
The patent applications disclosing selective estrogen receptor mediated modulators include WO2014165723, WO2014151899, WO2014141292, WO2014135834 and WO2014106848.
In order to achieve better therapeutic effects and to better meet the needs of the market, the inventors hope to develop a new generation of highly effective and low toxicity SERDs targeting the estrogen signaling pathway. The present invention provides a novel structure of a SERD, and it is found that the compounds with such a structure have good activity and show excellent ER receptor antagonism.